1. Field of the Invention
The subject invention generally pertains to sectional doors and more specifically to a counteraction system for such a door.
2. Description of Related Art
Sectional doors are commonly used as residential garage doors; however, they are also often used in warehouses and other industrial buildings. A sectional door typically includes a series of panels whose adjacent horizontal edges are connected by hinges. As the door opens or closes, the door panels travel along two lateral tracks. The tracks typically include a vertical section and an overhead section with a transitional curved section between the two. To close the door, the tracks guide the panels to a vertical position across the doorway. When the door opens, the hinges allow at least some of the panels to curve around onto the overhead section of the tracks. Such doors can be powered open and closed or moved manually.
To fit a sectional door underneath a standard 8-foot high ceiling of a typical residential garage, the vertical section of tracks is of limited height and the overhead section of tracks is generally horizontal. However, to take full advantage of generally higher ceilings in warehouses and other industrial buildings, a certain type of sectional door known as a xe2x80x9chigh-liftxe2x80x9d may be used. With a high-lift sectional door, the vertical section of tracks is extended and the overhead section may lie at an incline, such as a 15-degree incline from horizontal. The inclined overhead section and the extra vertical section provides greater clearance for material handling equipment, parts, and other equipment that may need to pass underneath the overhead tracks. With high-lift doors, one or more panels may store in the vertical and/or curved section of tracks when the door is at its fully open position.
To ease the operation of a sectional door, a torsion spring is often used to counteract the weight of the door panels. The spring strain increases as the door closes to compensate for the added weight of each additional door panel as the panels move off the horizontal tracks and into the vertical ones. Typically, the preload of the torsion spring is adjusted to be sufficient to hold the door fully open, yet not be so great that the spring prevents the door from ever staying closed under the door""s own weight. Sometimes it can be difficult to provide a torsion spring with just the right amount of preload.
A door""s torsion spring can be improperly adjusted during the initial installation of the door, or the spring""s preload can diminish as the spring ages. An inadequately preloaded spring may allow a sectional door to droop into the doorway or prevent the door from fully opening. An open door that is drooping can place its lowest door panel at an elevation where the panel is susceptible to being struck by vehicles, such large trucks, trailers, and forklifts. As a vehicle passes through the doorway, an upper edge of the vehicle may catch the lower edge of the door, and thus break or damage the door.
If the torsion spring were replaced by a simple counterweight to counter the door""s weight, the constant deadweight force exerted by the counterweight would not take into account the changing downward force of the door, as the door moves between its vertical and overhead positions. If the counterweight were of a weight that was just enough to hold the door open, such a counterweight would be insufficient to counter the total weight of the door panels when the door is closed. Thus, the weight of the door would make it difficult to open. Conversely, if the counterweight were of a weight that allowed the door to set gently down to its closed position (i.e., the counterweight being about equal to the accumulative weight of the door panels), that same weight may be excessive when the door approaches its open position, as much of the door""s weight is then supported by the overhead tracks. Such an excessive counterweight increases the force required to start pulling the door back down to its closed position.
Also, an excessive counterweight may slam the door against a hard stop at the door""s open position. To reduce that problem, conventional shock absorbers could be used to absorb the impact of the door hitting the stop. Such devices, however, are typically of an inline design with very limited travel for the amount of deceleration that the door may require.
In order to counter at least some of the weight of a sectional door, the door is provided with a counteraction system that includes a series of counterweights that apply a greater force on the door when the door is closed than when the door is open.
In some embodiments, the counterweight force applied to the door remains substantially constant when the door is near its fully closed position.
In some embodiments, the counterweight force applied to the door remains substantially constant when the door is near its fully open position.
In some embodiments, the counterweights are sequentially shed as the door opens.
In some embodiments, the counterweights are suspended from each other.
In some embodiments, the counterweights slide vertically within a tube.
In some embodiments, a rotatable drum couples the plurality of counterweights to the door.
In some embodiments, at least one counterweight helps hold the door in place when the door is at its fully open position.
In some embodiments, the counteraction system includes a brake system comprising a pliable member extending along a direction that traverses a direction that the door moves.
In some embodiments, the counterweight that helps hold the door open also exerts a force that deflects the brake system""s pliable member.